The instruments of the violin family may be descended in part from the
lira da braccio and the medieval
Byzantine lira. While the
cello (which developed from the
bass violin), the
viola and the
violin are indisputable members of the ancestral violin or
viola da braccio family, the
double bass's origins are sometimes called into question. The double bass is sometimes taken to be part of the
viol family, due to its sloping shoulders, its tuning, the practice of some basses being made with more than four strings and its sometimes flat back. Others point out that
correlation does not imply causation and say that these external similarities are either arbitrary or that they arose from causes other than a relationship to the viol family. They point to the internal construction of the double bass, which includes a
sound post and
bass bar like other violin family instruments as a more weighty piece of evidence than the external features. Its origins aside, it has historically been used as the lowest member of the violin family. All
string instruments share similar form, parts, construction and function, and the
viols bear a particularly close resemblance to the violin family. However, instruments in the violin family are set apart from viols by similarities in shape, tuning practice and history. Violin family instruments have four
strings each, are
tuned in fifths (except the double bass, which is tuned in fourths), are not
fretted and have four rounded bouts while always having a sound post and bass bar inside. In contrast, the viol family instruments usually have five to six strings with a fretted fingerboard, are tuned in fourths and thirds, often have sloping shoulders, and do not necessarily have a sound post or bass bar. bows ==Characteristics==